BER characteristics of π/4 DQPSK microwave subcarrier signals on optical fiber using Mach-Zehnder modulator nonlinear upconversion

The nonlinear transfer characteristic of a Mach-Zehnder modulator is utilized to up-convert an unmodulated electrical input signal at 4.1 GHz and a /spl pi//4 DQPSK modulated signal at 5.1 GHz to produce an unmodulated optical subcarrier at 16.4 GHz and a /spl pi//4 DQPSK modulated optical subcarrier at 17.4 GHz. Using a dc biased laser source at 1551 nm, the up-converted 50 Mb/s /spl pi//4 DQPSK optical subcarrier at 17.4 GHz is transmitted over up to 50 km of standard single-mode fiber and its BER is measured. The experiment demonstrates that the BER performance is degraded by less than 1 dB (electrical) by the optical up-conversion scheme.